Error while performing server's backup

hi, i have a repeated problem while the server performing its scheduled backup, i tried to run backup test and it as successfully done then i tried to make backup and successfully done too, but the problem occurred in the scheduled backup.

N.B

i have more than 7 servers but this is the only one who make error.

The error is :
(Backup DAG Incremental -- The job failed with the following error: The Backup Exec Agent for Microsoft Exchange was not used to create the last full backup of this database.  You must use the Exchange Agent to run a full backup before you run a differential or incremental backup).

kindly advice